A contrast agent useful for imaging a sample comprising a suspension in a medium acceptable for imaging (a) particles of a contrast agent possessing paramagnetic characteristics and (b) particles of a contrast agent possessing diamagnetic characteristics. Also disclosed is a method of imaging a sample which comprises introducing into the sample the above-described contrast agent and generating a substantially artifact-free image thereof. The combination of diamagnetic barium sulfate and superparamagnetic iron oxide (SPIO) in one suspension produces a macroscopic cancellation of positive and negative magnetic susceptibility components which eliminates susceptibility artifacts even with gradient echo pulse sequences. The relaxation properties which make the SPIO suspension a useful negative contrast agent are retained.
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